For several years, numerous studies have been conducted for replacing fossil energy sources by renewable energies. In particular, research has been oriented toward the creation of new fuels: agrofuels or ecofuels.
An ecofuel is a fuel that is produced from renewable organic materials of non-fossil origin.
There are various techniques for production of ecofuels, in particular the production of oil, alcohol, or gas fuels from plant or animal biomass, or industrial or community waste.
Currently, numerous agrofuels are being developed in the form of ethanol from fermentation of sugars originating from grains, wheat or corn, or beet scraps.
However, the development of these agrofuels poses significant problems, in particular because they compete directly with food cultivation and the production capacity of raw materials is limited compared to the very significant quantities of fuels that are consumed. It is estimated that only approximately 10% of the requirements could be met by this line.
In contrast, the available quantity of lignocellulosic compounds is very large and represents a potential of 40% of the fuel demand.
These lignocellulosic compounds comprise in particular wood, straw, plants originating from dedicated crops having a high level of dry material, agricultural co-products, collected plant wastes, and industrial or community waste.
The lignocellulosic biomass essentially consists of polysaccharides of cellulose and hemicelluloses, strongly linked to a lignin by covalent bond and hydrogen bond.
The production of ethanol from lignocellulosic compounds is done by hydrolysis of cellulose into molecules of glucose, simple sugars that are then fermented into ethanol by means of glycolysis. It requires a pretreatment for making cellulose accessible so as to facilitate its enzymatic hydrolysis.
In the known processes, lignocellulosic biomass is pretreated chemically for hydrolyzing hemicelluloses and making cellulose accessible.
In general, it involves a pretreatment by hydrolysis in a hot basic medium of the biomass for solubilizing hemicelluloses and a portion of lignin or in a hot weak acid medium for hydrolyzing hemicelluloses.
However, these known pretreatment methods are not satisfactory in terms of yield and require the use of concentrated products.